Pressure-sensitive adhesive tape is generally manufactured by coating onto a backing sheet a solution or emulsion of a pressure-sensitive adhesive polymer and heating the coating to drive off the volatile vehicle. Belgian Pat. No. 675,420 which was published May 16, 1966, concerns a process for making pressure-sensitive adhesive tape which evolves essentially no volatiles. While maintaining an inert atmosphere, a mixture of acrylic monomers and a photoinitiator is coated onto a backing sheet and then polymerized with ultraviolet radiation to a pressure-sensitive adhesive state.
U.S. Pat. No. 4,181,752 (Martens et al.) discloses a process for making pressure-sensitive adhesive tape which, like that of Belgian Pat. No. 675,420, involves the photopolymerization of acrylic monomers. While the Belgian patent discloses nothing of the specific intensity and the specific spectral distribution of the irradiation, the Martens patent discloses that these must be controlled in order to attain desirably high cohesive strength and also to attain high peel resistance. It teaches that the polymerizable mixture should be subjected to radiation in the near ultraviolet region at a rate of irradiation in the 300-400 nanometer wavelength range of not more than 7 milliwatts per square centimeter of the mass exposed. Any radiation shorter than 300 nanometers is limited to not more than about 10% of the energy in the 300-400 nanometers wavelength range. Because the same specific intensity and specific spectral distribution of the irradiation are preferred for the practice of the present invention, the disclosure of the Martens patent is here incorporated by reference.
Martens teaches that the pressure-sensitive adhesive layer may be crosslinked, particularly where it is desired to increase the cohesive strength of the adhesive without unduly affecting its compliance. This can be achieved by utilizing a photoactive crosslinking agent in conjunction with the photoinitiator. Preferred as the photoactive crosslinking agent are certain chromophore-substituted vinylhalomethyl-s-triazines such as 2,4-bis(trichloromethyl)-6-p-methoxystyryl-s-triazine which has the formula ##STR2## This compound is hereinafter called "MOST".
German Offenlegungsschrift No. 27 18 259 (Buhr) which was laid open Nov. 11, 1978, says that MOST and similar styryl-s-triazines are relatively complicated to prepare. It suggests that equally useful compounds can be prepared more easily, among which are ##STR3## wherein each of R.sub.1 and R.sub.2 may be, among other things, H or alkoxy, one of R.sub.1 and R.sub.2 may be Cl or Br, and m and n are integers from 0 to 3 and m+n does not exceed 5. U.S. Pat. No. 4,189,323 is issentially identical to the Offenlegungsschrift.